Application of a Mixed-Ligand Metal–Organic Framework in Photocatalytic CO2 Reduction, Antibacterial Activity and Dye Adsorption

In this paper, a known mixed-ligand MOF {[Co2(TZMB)2(1,4-bib)0.5(H2O)2]·(H2O)2}n (compound 1) was reproduced, and its potential application potential was explored. It was found that compound 1 had high photocatalytic activity for CO2 reduction. After 12 h of illumination, the formation rate of CO, which is the product of CO2 reduction by compound 1, reached 3012.5 μmol/g/h. At the same time, compound 1 has a good antibacterial effect on Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Candida albicans (C. albicans), which has potential research value in the medical field. In addition, compound 1 can effectively remove Congo Red from aqueous solutions and achieve the separation of Congo red from mixed dye solutions.


Introduction
A porous solid material is formed by the self-assembly of an inorganic metal ion (or cluster) with some organic ligand, which we define as a metal-organic framework, or MOF. Generally, in metal-organic skeletal materials, there is an interaction between the metal and the organic ligand, which is also referred to as a coordination polymer, CP. MOFs can be synthesized by selecting organic ligands containing different atoms such as O, N, P and S, changing the central metal atom and coordination mode, and controlling other external environmental factors including solvent, temperature, pH, etc., to tune the network structure, shape and properties of the compound. In recent years, with the increasing number of synthesized MOFs, exploring its excellent performance in various fields has become the direction of recent researchers [1][2][3][4][5].
The CO 2 levels in the atmosphere have increased dramatically due to phenomena such as industrial production and exhaust emissions, while at the same time, the human exploitation of nature has reduced the absorption of CO 2 by trees, thus exacerbating the greenhouse effect. The natural way to consume CO 2 is through photosynthesis in green plants, and photocatalytic CO 2 reduction is the closest redox reaction to natural photosynthesis. This technology converts CO 2 into energy products such as CH 4 , CH 3 OH and CH 3 COOH through photocatalytic reactions. It has the advantages of being green and efficient, having a low energy consumption and having no secondary pollution, thus becoming an ideal solution to environmental pollution. As might be expected from photosynthesis, photocatalytic reduction systems require substances that absorb light (photosensitizers), substances that provide electrons (electronic sacrificial agents) and substances that enable the catalytic reaction to proceed efficiently (catalysts). The catalysts that have been reported for use in photocatalytic CO 2 reduction systems are semiconductor materials, organic photosensitive dyes and precious metal compounds. However, their application is limited by their low light absorption efficiency, high price and lack of availability. Metal-organic frameworks (MOFs) are porous and have a large specific surface area, which allows for of the adsorbent in water, chloroform and dimethylformamide (DMF) over a period of one year, and the results show that UiO-66 is a chemically stable MOF. It was successfully synthesized and used for the removal of anionic and cationic dyes from aqueous solutions [30]. The study by Kumar et al. covers the application of MOFs in wastewater treatment/purification, aiming to address the treatment of the most persistent chemicals in water. The applicability of MOFs was evaluated for dynamic and low-cost wastewater treatment/purification options in combination with their advanced functions (adsorption, photodegradation/catalysis, separation and sensing). In order to further improve the practicality of MOF technology in WWT, significant efforts were invested in verifying its capacity and reliability for the treatment of various organic pollutants in water [31]. Zhan and researchers carried out adsorption experiments using an isotopically structured zirconium-based metal-organic backbone (Zr-MOF), which can be used for adsorption studies due to its good stability at high temperatures and pressures, as well as its chemical stability to acids and bases. The adsorption performance of Zr-MOF depends on the pore size of the MOF and the surrounding environment. In this study, the Zr-MOF material remained stable as the size changed and the adsorption proceeded, reaching an optimum adsorption state at 235 mg/g. During the adsorption process, physical adsorption occurs on the MOF surface, while chemisorption occurs in the form of dye molecules binding to the active site. It was eventually concluded that the larger the pore size, the greater the adsorption capacity, which is a contribution that provides new ideas for wastewater treatment problems [32].
In this paper, a known mixed-ligand MOF ({[Co 2 (TZMB) 2 (1,4-bib) 0.5 (H 2 O) 2 ]·(H 2 O) 2 } n ) [1] (compound 1) was reproduced, and its potential application potential was explored. It was found that the compound has a good performance of the CO 2 photocatalytic reduction of CO. Under the optimal reaction conditions after 12 h of illumination, the formation rate of CO reaches 3012.5 µmol/g/h. Through the antibacterial test, it can be found that compound 1 completely inhibits the growth of S. aureus, E. coli and C. albicans within 24 h. In addition, compound 1 can effectively remove Congo Red from aqueous solutions and achieve the separation of Congo red from mixed dye solutions.

Photocatalytic CO 2 Reduction
The nature of photocatalytic CO 2 reduction is a redox reaction in which CO 2 is reduced to HCOOH, CH 3 OH or gaseous products such as CO, CH 4 , H 2 and C 2 H 4 in the presence of a reducing agent. The reaction products were qualitatively detected via gas chromatography as CO ( Figure 1). The choice of solvent is critical to the reaction system, and the solubility of the compound in the solvent will directly affect the CO 2 reduction efficiency. In this paper, three reagents, DMF, DMA and CH 3 CN, were chosen to be mixed with water as reaction solvents. All three solvents have a good solubility and stability for a variety of substances. The pressure of the photocatalytic reduction reaction system was 1 MPa with compound 1 as catalyst, bipyridylruthenium (Ru) as a photosensitizer and TEOA as an electron sacrificial agent.
Further, experiments were carried out regarding the ideal type of reaction solvent and its ratio, the ideal type and amount of electron sacrificial agent, the ideal amount of photosensitizer and the ideal amount of compound ( Figure 2). The experimental results show that 10 mg of compound 1, 30 mg of photosensitizer (Ru) and 6 mL of solvent (DMA:H 2 O:TEOA = 4:1:1) were the optimum reaction conditions for the reaction system.  According to the optimum reaction conditions, the photocatalytic reaction was carried out. Firstly, carbon dioxide was continuously injected into the top-illuminated photocatalytic reactor to eliminate the interference of impurities. After about 15 min, we closed the valve and continued to introduce CO2 so that the pressure in the reaction ke le could reach 1 MPa. The PLS-SXE300D xenon lamp with a 420 nm filter was irradiated continuously for 12 h, and the samples were analyzed via gas chromatography every 3 h, and the cycle was repeated more than three times to prove its accuracy.   According to the optimum reaction conditions, the photocatalytic reaction ried out. Firstly, carbon dioxide was continuously injected into the top-illumina tocatalytic reactor to eliminate the interference of impurities. After about 15 closed the valve and continued to introduce CO2 so that the pressure in the reacti According to the optimum reaction conditions, the photocatalytic reaction was carried out. Firstly, carbon dioxide was continuously injected into the top-illuminated photocatalytic reactor to eliminate the interference of impurities. After about 15 min, we closed the valve and continued to introduce CO 2 so that the pressure in the reaction kettle could reach 1 MPa. The PLS-SXE300D xenon lamp with a 420 nm filter was irradiated continuously for 12 h, and the samples were analyzed via gas chromatography every 3 h, and the cycle was repeated more than three times to prove its accuracy.
It is easy to see from Figure 3 that the CO production rate increased linearly with time. The rate of product formation per unit mass of sample was calculated using the formula PV = nRT, and the product CO produced by the photocatalytic reduction of carbon dioxide in compound 1 was as high as 3012.5 µmol/g/h (P = 1 MPa, T = 313.15 K, R = 8.31 J/(mol·K), V was calculated from the ratio of the real-time peak area of the product to the peak area of 1 mL of standard gas). It is easy to see from Figure 3 that the CO production rate increased linearly with time. The rate of product formation per unit mass of sample was calculated using the for mula PV = nRT, and the product CO produced by the photocatalytic reduction of carbon dioxide in compound 1 was as high as 3012.5 µmol/g/h (P = 1 MPa, T = 313.15 K, R = 8.31 J/(mol·K), V was calculated from the ratio of the real-time peak area of the product to th peak area of 1 mL of standard gas). After that, the control test was carried out for compound 1. The results show that th formation rate of CO is negligible without the presence of complexes, (Ru) and TEOA respectively (Table 1). In dark conditions and without CO2, CO will not be generated. Thi shows that each component in the system is indispensable for the photocatalytic reduction of CO2, and the existence of compound 1 greatly increases the rate of CO production, in dicating that compound 1 plays a crucial role in the reaction system. After the experiment the recovered compound 1 was analyzed via powder XRD, and the results show that com pound 1 had good stability.

Antibacterial Properties
In this paper, S. aureus (ATCC 6538), E. coli (CMCC 44102) and C. albicans (ATCC After that, the control test was carried out for compound 1. The results show that the formation rate of CO is negligible without the presence of complexes, (Ru) and TEOA, respectively (Table 1). In dark conditions and without CO 2 , CO will not be generated. This shows that each component in the system is indispensable for the photocatalytic reduction of CO 2 , and the existence of compound 1 greatly increases the rate of CO production, indicating that compound 1 plays a crucial role in the reaction system. After the experiment, the recovered compound 1 was analyzed via powder XRD, and the results show that compound 1 had good stability.

Antibacterial Properties
In this paper, S. aureus (ATCC 6538), E. coli (CMCC 44102) and C. albicans (ATCC 10231) were selected as experimental objects. The experimental instruments, prepared LB medium and PDB medium were sterilized with high-pressure steam and transferred to an ultra-clean table. After inoculation, they were cultured in a shaker at 37 • C. After leaving it overnight, the bacterial liquid was diluted 100 times with the culture medium for later use. We prepared a certain amount of solid culture medium. A proper amount of S. aureus and E. coli diluted to 10 7 CFU/mL were coated in LB medium, and C. albicans were coated in PDB medium evenly. After the bacterial liquid was absorbed, the circular paper was soaked with different concentrations (1 mg/mL, 5 mg/mL) of the compound and then put into the culture medium. Blank and heterocyclic multidentate carboxylic acid ligands were used as the controls. The treated plate was cultured in a constant temperature incubator at 37 • C for 24 h. We then observed and recorded the diameter of the suppression ring.
The control experiment showed that metal salts and mixed ligands had no antibacterial effect on the bacterial solution. When the concentration of the solution of compound 1 was 5 mg/mL, the diameter of the bacteriostatic circle for S. aureus reached 14 mm, and the minimum inhibitory concentration MIC was 500 µg/mL (Figure 4a). For E. coli, the diameter of the bacteriostatic circle was 11 mm, and the MIC was 400 µg/mL (Figure 4b).
For C. albicans, the diameter of the bacteriostatic circle was 11 mm, and the MIC was 200 µg/mL (Figure 4c).
Molecules 2023, 28, x FOR PEER REVIEW 6 of 13 coated in PDB medium evenly. After the bacterial liquid was absorbed, the circular paper was soaked with different concentrations (1 mg/mL, 5 mg/mL) of the compound and then put into the culture medium. Blank and heterocyclic multidentate carboxylic acid ligands were used as the controls. The treated plate was cultured in a constant temperature incubator at 37 °C for 24 h. We then observed and recorded the diameter of the suppression ring.
The control experiment showed that metal salts and mixed ligands had no antibacterial effect on the bacterial solution. When the concentration of the solution of compound 1 was 5 mg/mL, the diameter of the bacteriostatic circle for S. aureus reached 14 mm, and the minimum inhibitory concentration MIC was 500 µg/mL (Figure 4a). For E. coli, the diameter of the bacteriostatic circle was 11 mm, and the MIC was 400 µg/mL (Figure 4b).
For C. albicans, the diameter of the bacteriostatic circle was 11 mm, and the MIC was 200 µg/mL (Figure 4c). We prepared different concentrated solutions of compound 1 in the LB medium and added appropriate amounts of diluted E. coli and S. aureus, respectively; we prepared different concentrated solutions of compound 1 in the PDB medium and added appropriate amounts of diluted C. albicans. The bacterial solution was placed in a shaker at 37 °C, and the absorbance at 600 nm (OD600) was measured every 3 h using an enzyme marker to obtain the growth curve of the strains. It can be seen from the growth curve that the bacterial solution of the blank control group increased exponentially. For S. aureus ( Figure  5a), with the increase in the concentration of compound 1, the bacteriostatic effect was gradually enhanced. When the concentration of the complex was 500 µg/mL, the growth of the bacterial solution was completely inhibited. For E. coli (Figure 5b), the growth of the bacterial solution was also completely inhibited when the concentration of 1 reached 400 µg/mL. For C. albicans (Figure 5c), when the concentration of 1 was 200µg/mL, the growth of the bacterial solution was completely inhibited. We prepared different concentrated solutions of compound 1 in the LB medium and added appropriate amounts of diluted E. coli and S. aureus, respectively; we prepared different concentrated solutions of compound 1 in the PDB medium and added appropriate amounts of diluted C. albicans. The bacterial solution was placed in a shaker at 37 • C, and the absorbance at 600 nm (OD600) was measured every 3 h using an enzyme marker to obtain the growth curve of the strains. It can be seen from the growth curve that the bacterial solution of the blank control group increased exponentially. For S. aureus (Figure 5a), with the increase in the concentration of compound 1, the bacteriostatic effect was gradually enhanced. When the concentration of the complex was 500 µg/mL, the growth of the bacterial solution was completely inhibited. For E. coli (Figure 5b), the growth of the bacterial solution was also completely inhibited when the concentration of 1 reached 400 µg/mL. For C. albicans (Figure 5c), when the concentration of 1 was 200µg/mL, the growth of the bacterial solution was completely inhibited.

Dye Adsorption
Currently, with the rapid development of the economy, more and more environmental pollution problems have come along, among which dye pollution in water is a big aspect. Since compound 1 was very stable in the aqueous solution and had large pores in its structure, three organic dyes were selected to test its dye adsorption performance, which were Congo Red (CR), Methylene Blue (MB) and Rhodamine B (RhB).
First, 10 mg of compound 1 was added to 50 mL (5 × 10 −5 mol·L −1 ) of the dye aqueous solution. Subsequently, the UV spectra of the mixture at different time intervals were recorded after the mixture reached the adsorption dissociation equilibrium. The UV spectral analysis in Figure 6a and the photos before and after adsorption show that compound 1 has a fast adsorption capacity for CR, while it has almost no adsorption capacity for the other two dyes. In ten minutes, the removal of CR by compound 1 can reach 99% (Equation (S1), ESI †).
Through the adsorption capacity experiment (Figure 6b), it can be found that the adsorption capacity of compound 1 to CR can reach 1194 mg·g −1 (Equation (S2)). The unique adsorption capacity of compound 1 is mainly due to the electrostatic interaction between its pores and CR molecules. A release test was also carried out to confirm the regeneration capacity of the adsorbent. Compound 1 was placed in a methanol solution and released after the adsorption of CR (5 × 10 −5 mol·L −1 ). For compound 1, the CR was released with an efficiency of 99% ( Figure S8, ESI †). The XRD data show that the structure of compound 1 did not change before and after the experiment ( Figure S9, ESI †). This indicates that compound 1 has good regeneration performance during the adsorption-desorption process.

Dye Adsorption
Currently, with the rapid development of the economy, more and more environ-mental pollution problems have come along, among which dye pollution in water is a big aspect. Since compound 1 was very stable in the aqueous solution and had large pores in its structure, three organic dyes were selected to test its dye adsorption performance, which were Congo Red (CR), Methylene Blue (MB) and Rhodamine B (RhB).
First, 10 mg of compound 1 was added to 50 mL (5 × 10 −5 mol·L −1 ) of the dye aqueous solution. Subsequently, the UV spectra of the mixture at different time intervals were recorded after the mixture reached the adsorption dissociation equilibrium. The UV spectral analysis in Figure 6a and the photos before and after adsorption show that compound 1 has a fast adsorption capacity for CR, while it has almost no adsorption capacity for the other two dyes. In ten minutes, the removal of CR by compound 1 can reach 99% (Equation (S1), ESI †). In addition, the UV-Vis spectroscopic analysis and before and after photos of the adsorption reveal that compound 1 showed almost no adsorption of the cationic dyes of MB and RhB ( Figure S10, ESI †).
To further investigate the selective adsorption ability of compound 1 on CR, CR/MB and CR/RhB were mixed to obtain brown and pink solutions, respectively, and 10 mg of Through the adsorption capacity experiment (Figure 6b), it can be found that the adsorption capacity of compound 1 to CR can reach 1194 mg·g −1 (Equation (S2)). The unique adsorption capacity of compound 1 is mainly due to the electrostatic interaction between its pores and CR molecules. A release test was also carried out to confirm the regeneration capacity of the adsorbent. Compound 1 was placed in a methanol solution and released after the adsorption of CR (5 × 10 −5 mol·L −1 ). For compound 1, the CR was released with an efficiency of 99% ( Figure S8, ESI †). The XRD data show that the structure of compound 1 did not change before and after the experiment ( Figure S9, ESI †). This indicates that compound 1 has good regeneration performance during the adsorption-desorption process.
In addition, the UV-Vis spectroscopic analysis and before and after photos of the adsorption reveal that compound 1 showed almost no adsorption of the cationic dyes of MB and RhB ( Figure S10, ESI †).
To further investigate the selective adsorption ability of compound 1 on CR, CR/MB and CR/RhB were mixed to obtain brown and pink solutions, respectively, and 10 mg of compound 1 was added. The solutions showed blue and pink colors after 20 min, respectively, indicating an effective selective adsorption of the mixed dyes by compound 1. The CR removal reached 84% (CR/MB) and 85% (CR/RhB) (Figure 7a,b). In addition, the UV-Vis spectroscopic analysis and before and after photos of the adsorption reveal that compound 1 showed almost no adsorption of the cationic dyes of MB and RhB ( Figure S10, ESI †).
To further investigate the selective adsorption ability of compound 1 on CR, CR/MB and CR/RhB were mixed to obtain brown and pink solutions, respectively, and 10 mg of compound 1 was added. The solutions showed blue and pink colors after 20 min, respectively, indicating an effective selective adsorption of the mixed dyes by compound 1. The CR removal reached 84% (CR/MB) and 85% (CR/RhB) (Figure 7a,b). The above experiments demonstrated the potential selective separation ability of compound 1 for the CR dye, and it was therefore used as a stationary phase for the column to more clearly express its ability to effectively remove CR from aqueous solutions. In the experiment, a pipe e was used to simulate the chromatographic column, and 100 mg of compound 1 was filled in it to filter the mixed solutions of CR, CR/MB and CR/RhB. As shown in Figure 8, after filtration, the CR dyes were all adsorbed by compound 1, with the single dyes showing no color, and the mixed dyes showing another color. Thus, compound 1 shows a potential application in the efficient separation of CR from mixed dye solutions. The above experiments demonstrated the potential selective separation ability of compound 1 for the CR dye, and it was therefore used as a stationary phase for the column to more clearly express its ability to effectively remove CR from aqueous solutions. In the experiment, a pipette was used to simulate the chromatographic column, and 100 mg of compound 1 was filled in it to filter the mixed solutions of CR, CR/MB and CR/RhB. As shown in Figure 8, after filtration, the CR dyes were all adsorbed by compound 1, with the single dyes showing no color, and the mixed dyes showing another color. Thus, compound 1 shows a potential application in the efficient separation of CR from mixed dye solutions.

Materials and Instrumentation
Powder X-ray diffraction (PXRD) data were recorded on the D2 PHASER A26-X XRD diffractometer. The IR spectra (4000-400 cm −1 ) were obtained from KBr pellets wit an FTIR Nexus spectrophotometer. Elemental analyses were performed on a PerkinElme 240 C analyzer. Spectra Max Plus 384 microplate reader was used to determine OD 600 o bacterial liquid. The ultraviolet absorption spectrum was collected using Cary 300 spec trophotometer. The composition and content of CO2 reduction products were recorde using the gas chromatograph (GC-7920).

Synthesis of MOF
In this paper, an MOF with the same structure was synthesized using a synthesi method similar to that used by the Hu team [1]. A mixture of Co(NO3)2·6H2O (32.1 mg, 0. mmol), 1,4-bib (21 mg, 0.1 mmol) and H2TZMB (32.3 mg, 0.1 mmol) was dissolved in 1 mL of H2O solvent ( Figure S1, ESI †). After stirring, the mixture was sealed in a 25 mL Par Teflon-lined stainless-steel autoclave under autogenous pressure and heated at 160 °C fo three days. Then, after slow cooling to room temperature at 20 °C·h −1 , large quantities o purple bulk crystals were obtained, and the crystals were filtered off, washed with abso lute ethyl alcohol and dried under ambient conditions. The final yield collected was 5 wt% on H2TZMB ligand. Elemental analysis calcd. for C23H15O4N5Co  Figure S2 shows the interpenetrating structure of compound 1 (ESI †

Powder X-ray Diffraction (PXRD)
Compound 1 [1] was synthesized according to the synthetic route in the literature and its XRD data were mildly similar to those in the literature, indicating that a high pu rity compound 1 was obtained (Figure 9).

Materials and Instrumentation
Powder X-ray diffraction (PXRD) data were recorded on the D2 PHASER A26-X1 XRD diffractometer. The IR spectra (4000-400 cm −1 ) were obtained from KBr pellets with an FTIR Nexus spectrophotometer. Elemental analyses were performed on a PerkinElmer 240 C analyzer. Spectra Max Plus 384 microplate reader was used to determine OD 600 of bacterial liquid. The ultraviolet absorption spectrum was collected using Cary 300 spectrophotometer. The composition and content of CO 2 reduction products were recorded using the gas chromatograph (GC-7920).

Synthesis of MOF
In this paper, an MOF with the same structure was synthesized using a synthesis method similar to that used by the Hu team [1]. A mixture of Co(NO 3 ) 2 ·6H 2 O (32.1 mg, 0.1 mmol), 1,4-bib (21 mg, 0.1 mmol) and H 2 TZMB (32.3 mg, 0.1 mmol) was dissolved in 10 mL of H 2 O solvent ( Figure S1, ESI †). After stirring, the mixture was sealed in a 25 mL Parr Teflon-lined stainless-steel autoclave under autogenous pressure and heated at 160 • C for three days. Then, after slow cooling to room temperature at 20 • C·h −1 , large quantities of purple bulk crystals were obtained, and the crystals were filtered off, washed with absolute ethyl alcohol and dried under ambient conditions. The final yield collected was 54 wt% on H 2 TZMB ligand. Elemental analysis calcd. for C 23 Figure S2 shows the interpenetrating structure of compound 1 (ESI †).

Powder X-ray Diffraction (PXRD)
Compound 1 [1] was synthesized according to the synthetic route in the literature, and its XRD data were mildly similar to those in the literature, indicating that a high purity compound 1 was obtained (Figure 9).

Optimum Reaction Conditions of Photocatalysis
In the reaction system consisting of complex catalyst, photosensitizer, sacrificial agent and solvent, the reaction product is qualitatively detected as CO via gas chromatography. In order to test the optimal reaction conditions, the effects of different solvents and their proportions, the electron sacrificing agents and their proportions, the number of photosensitizers and the number of compounds on the reaction system were discussed in the experiment to determine the final experimental conditions. The above experiments determined the optimal reaction conditions of the reaction system to be the following: 10 mg of compound 1, 40 mg of photosensitizer (Ru), 6 mL of solvent (DMA: H2O: TEOA = 4:1:1) and the CO2 pressure of 1 MPa. A controlled test was also carried out, and the results show that each component of the system was important for hanging photocatalytic CO2 reduction and that the addition of the complexes greatly increased the rate of CO production. We show the stability performance of compound 1 before and after the experiment by comparing the PXRD and TGA of compound 1 before and after CO2 reduction in Figures  S3 and S4, ESI †.

Bacterial Incubation and Bacteriostatic Circle Experiment
The experimental apparatus and the configured LB medium and PDB medium were transferred to the ultraclean table after autoclaving, and then S. aureus (ATCC 6538), E. coli (CMCC 44102) and C. albicans (ATCC 10231) were incubated in a shaker at 37 °C. The overnight bacterial liquid was diluted 100 times with the culture medium for standby.
In the bacteriostasis circle experiment, appropriate amounts of S. aureus and E. coli diluted to 107 CFU/mL by the culture medium were evenly smeared in the LB culture medium, and C. albicans were smeared in the PDB culture medium. After the bacterial solution was absorbed, the round paper of the fully soaked compound 1 was put into the culture medium. The blank and mixed ligands were used as control. Then, we put them in a constant temperature incubator at 37 °C for 24 h and observed and recorded the diameter of the inhibition ring.

MIC Determination and Growth Curve Experiment
The bacterial solution after overnight culture was diluted to 10 5 CFU/mL for standby. We diluted the compound 1 solution prepared with LB and PDB medium on a 96-well plate continuously (the volume was 100 µL), and added 100 µL of diluted bacterial solution. We put the treated pore plate in a constant temperature incubator at 37 °C, and obtained the MIC results after 24 h (Figures S5-S7, ESI †).
The LB medium was used to prepare different concentrations of the compound solution, and appropriate amounts of diluted E. coli and S. aureus were added, respectively. PDB medium was used to prepare different concentrations of compound solution, and an

Optimum Reaction Conditions of Photocatalysis
In the reaction system consisting of complex catalyst, photosensitizer, sacrificial agent and solvent, the reaction product is qualitatively detected as CO via gas chromatography. In order to test the optimal reaction conditions, the effects of different solvents and their proportions, the electron sacrificing agents and their proportions, the number of photosensitizers and the number of compounds on the reaction system were discussed in the experiment to determine the final experimental conditions. The above experiments determined the optimal reaction conditions of the reaction system to be the following: 10 mg of compound 1, 40 mg of photosensitizer (Ru), 6 mL of solvent (DMA: H 2 O: TEOA = 4:1:1) and the CO 2 pressure of 1 MPa. A controlled test was also carried out, and the results show that each component of the system was important for hanging photocatalytic CO 2 reduction and that the addition of the complexes greatly increased the rate of CO production. We show the stability performance of compound 1 before and after the experiment by comparing the PXRD and TGA of compound 1 before and after CO 2 reduction in Figures S3 and S4, ESI †.

Bacterial Incubation and Bacteriostatic Circle Experiment
The experimental apparatus and the configured LB medium and PDB medium were transferred to the ultraclean table after autoclaving, and then S. aureus (ATCC 6538), E. coli (CMCC 44102) and C. albicans (ATCC 10231) were incubated in a shaker at 37 • C. The overnight bacterial liquid was diluted 100 times with the culture medium for standby.
In the bacteriostasis circle experiment, appropriate amounts of S. aureus and E. coli diluted to 107 CFU/mL by the culture medium were evenly smeared in the LB culture medium, and C. albicans were smeared in the PDB culture medium. After the bacterial solution was absorbed, the round paper of the fully soaked compound 1 was put into the culture medium. The blank and mixed ligands were used as control. Then, we put them in a constant temperature incubator at 37 • C for 24 h and observed and recorded the diameter of the inhibition ring.

MIC Determination and Growth Curve Experiment
The bacterial solution after overnight culture was diluted to 10 5 CFU/mL for standby. We diluted the compound 1 solution prepared with LB and PDB medium on a 96-well plate continuously (the volume was 100 µL), and added 100 µL of diluted bacterial solution. We put the treated pore plate in a constant temperature incubator at 37 • C, and obtained the MIC results after 24 h (Figures S5-S7, ESI †).
The LB medium was used to prepare different concentrations of the compound solution, and appropriate amounts of diluted E. coli and S. aureus were added, respectively. PDB medium was used to prepare different concentrations of compound solution, and an appropriate amount of diluted C. albicans was added. We put the bacterial solution into a shaker at 37 • C, and measured its absorbance at 600 nm wavelength with a microplate reader every 3 h to obtain the growth curve of the bacterial species.

Conclusions
In this paper, a known compound was synthesized, and its photocatalytic properties, antibacterial properties and dye adsorption properties were investigated. In the photocatalysis experiment, a novel photocatalysis carbon dioxide reduction system was successfully constructed. In 12 h, the average generation rate of CO can reach 3012.5 µmol/g/h. At the same time, the high concentration of compound 1 can completely inhibit the growth of S. aureus, E. coli and C. albicans within 24 h. In addition, at one hour, the adsorption capacity of compound 1 to CR can reach 1194 mg·g −1 and can achieve a rapid separation of CR in mixed dye solutions. The above experiments show that compound 1 has potential applications in photocatalytic CO 2 reduction, solid antibacterial activity and dye adsorption.
Supplementary Materials: The following are available online at https://www.mdpi.com/article/ 10.3390/molecules28135204/s1, Figure S1. Molecular structure of ligands, Figure S2. (a) The coordination environment of the Co(II) ions in compound 1. (b,c) View of 3D net structure. (d) View of 4-fold interpenetrated framework, Figure S3. XRD patterns of the MOF (a represents theoretical XRD, b represents experimental XRD, and c represents XRD after three cycles), Figure S4. TGA patterns of the MOF (a represents experimental TGA, and b represents TGA after three cycles), Figure S5. Changes of MOF solution with different concentration on S. aureus in 24 h, Figure S6. Changes of MOF solution with different concentration on E. coli in 24 h, Figure S7. Changes of MOF solution with different concentration on C. albicans in 24 h, Figure S8. Adsorption-desorption curve for CR (before: 5 × 10 −5 CR; after: desorption for 1 by methanol), Figure S9.